Conventionally, for example, in the field of optical technology to which liquid crystal display devices and the like belong, it has been suggested to use a light diffusion film which can diffuse an incident light coming from a particular direction into particular directions, while directly transmitting an incident light coming from other directions.
A variety of forms of such a light diffusion film are known; however, in particular, a light diffusion film having, within the film, a louver structure in which plural plate-shaped regions having different refractive indices are alternately arranged in one arbitrary direction along the film plane, has been widely used.
Furthermore, regarding another type of light diffusion film, a light diffusion film having, within the film, a columnar structure in which plural pillar-shaped objects having a relatively high refractive index are arranged to stand close together in regions having a relatively low refractive index, has been widely used.
Meanwhile, it is known that such a light diffusion film having a louver structure or a columnar structure is obtained by irradiating a coating layer that is formed by applying a composition for light diffusion film containing two or more kinds of polymerizable compounds having different refractive indices into a film form, with active energy radiation by a predetermined method.
That is, a light diffusion film having a predetermined internal structure can be obtained by curing the coating layer while subjecting the two or more kinds of polymerizable compounds in the coating layer to phase separation, by irradiating the coating layer with predetermined active energy radiation having a controlled direction of propagation.
Therefore, in order to obtain a high-quality light diffusion film having a more well-defined internal structure and having satisfactory incident angle dependency in transmission and diffusion of light, there has been suggested a composition for light diffusion film, which can achieve phase separation of two or more kinds of polymerizable compounds more efficiently, and can photocure the polymerizable compounds more stably (for example, Patent Documents 1 and 2).
That is, Patent Document 1 discloses a composition for anisotropic light diffusion film including a biphenyl compound represented by the following Formula (11) as component (A), and a polymerizable compound having a weight average molecular weight value within the range of 3,000 to 20,000 as component (B), characterized in that the content of the component (A) is adjusted to a value within the range of 25 parts to 400 parts by weight relative to 100 parts by weight of the component (B):
wherein in Formula (11), Ra1 to Ra10 are respectively independent of one another; and at least one of Ra1 to Ra10 represents a substituent represented by the following Formula (12), while the others each represent any one substituent selected from a hydrogen atom, a hydroxyl group, a carboxyl group, an alkyl group, an alkoxy group, a halogenated alkyl group, a hydroxyalkyl group, a carboxyalkyl group, and a halogen atom;
wherein in Formula (12), Ra11 represents a hydrogen atom or a methyl group; the number of carbon atoms p represents an integer from 1 to 4; and the number of repetition q represents an integer from 1 to 10.
Furthermore, Patent Document 2 discloses a composition for an anisotropic light diffusion film, which includes a (meth)acrylic acid ester containing plural aromatic rings as component (A); and a urethane (meth)acrylate having a weight average molecular weight value within the range of 3,000 to 20,000 as component (B), characterized in that the urethane (meth)acrylate as the component (B) is a compound derived from the following components (a) to (c) as constituent components and is composed of the components at a molar ratio of component (a):component (b):component (c)=1 to 5:1:1 to 5, and the content of the component (A) is adjusted to a value within the range of 25 parts to 400 parts by weight relative to 100 parts by weight of the component (B):
(a) a compound containing two isocyanate groups via an aliphatic ring;
(b) a polyalkylene glycol; and
(c) a hydroxyalkyl (meth)acrylate.